Mangrove Encroachment Alters Decomposition Rate in Saltmarsh Through Changes in Litter Quality
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Mangrove Encroachment Alters Decomposition Rate in Saltmarsh Through Changes in Litter Quality Lorae´ T. Simpson,1,2,3,5* Julia A. Cherry,2 Rachel S. Smith,4 and Ilka C. Feller3 1 Smithsonian Marine Station, Fort Pierce, Florida 34949, USA; 2University of Alabama, Tuscaloosa, Alabama 35487, USA; Smithsonian Environmental Research Center, Edgewater, Maryland 21037, USA; 4University of Virginia, Charlottesville, Virginia 22903, USA; 5Present address: Present Address: Florida Oceanographic Society, 890 NE Ocean Blvd, Stuart, Florida 34996, USA
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ABSTRACT Global climate change is driving the expansion of mangroves into saltmarsh habitat, which may alter the rate and magnitude of organic matter decomposition and nutrient cycling due to differences in the structural complexity, litter quality, and other ecophysiological traits of foundation species. This work quantified and compared aboveground litter decomposition of the range-expanding mangrove, Avicennia germinans, and resident saltmarsh cordgrass, Spartina alterniflora, and decomposition of a standard substrate belowground, in the saltmarsh and saltmarsh-mangrove ecotone habitat along the Atlantic coast of Florida, USA. Plant and soil fractions were tested for natural abundances of d13C and d15N stable isotopes to elucidate soil nutrient sources. Although aboveground decomposition rates differed between marsh and mangrove species due to differences in litter quality, decomposition rates did not vary between saltmarsh and ecotonal
habitats. Decay rates were higher for A. germinans leaf litter (0.007 ± 0.0003 k day-1) than for S. alterniflora (0.004 ± 0.0003 k day-1) regardless of habitat, which suggests that increasing inputs of A. germinans litter with encroachment may increase nutrient availability through rapid turnover. Furthermore, belowground decomposition was similar between habitats (0.015 ± 0.0008 k day-1), 13 15 whereas soil d C and d N stable isotopes differed significantly. Collectively, these results suggest that mangrove encroachment may not modify the environmental factors driving decomposition, but alterations in foundation plant species may ultimately alter nutrient cycling within habitats through shifts in litter quality. Key words: Decay rate; Litter quality; Stable isotopes; Mangrove encroachment; d15N; Foundation species.
HIGHLIGHTS Received 22 June 2020; accepted 17 August 2020 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00554-z) contains supplementary material, which is available to authorized users. Author’s Contribution LTS and ICF designed the study; LTS performed the research; LTS and JAC analyzed the data; RSS contributed additional methods and data; LTS, JAC, RSS and ICF wrote the paper. *Corresponding author; e-mail: [email protected]
Changes in foundation species cover will alter aboveground decomposition rates. Species litter quality, not habitat structure, drives aboveground decomposition rates. Habitat structure did not affect belowground decomposition ra
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